Method of and apparatus for electroplating



Oct- 2, .1951 l H. J. READING 2,569,577

METHOD OF' AND APPARATUS FOR ELECTROPLATING Filed May 9, 1947 2 sheets-sheet 1 H am I Will IN VEN TOR.

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Oct. 2, -I J. READING y METHOD 0F AND APPARATUS FOR ELECTROPLATING 2 sheets-sheet' 2 Filed May lsa, 41941' ||J||| PN WNIIINI lll Tini INVENToR /MRRVJ keno/N6.

Patented Oct. 2, 1951 UNITED orifice;A

Harry J. Reading;''Steubenvill Ohio', as'si'gnorrto National:i SteelffCorporation," a 'corporation of Delaware 'v AplieatioirMa-'y 9; 1947, serial Noi '147,006l f 11 claims. (c1. amaze 'I'he presentinventionrelatstolimprovements" in! a "method offandlapparatu's -for electrodepo'siting a protective meta-lv coating'fontoat least" orief'surface of a :continuously moving-'strip' ofconductive base metalv and more particularly relates fito 'improvements fin j circulatingv and 'dislchargingreplenishing 'sol-iitioninto an electro' plating ce'llv of `the? type use'd' for' depositing -pro" f gressively Va metal Acoating on the bottom'fsurfaceof a horizontally and continuously moving metal strip.,`

The present?` invention will be 'f'describe'd more particularlyYA inlconnectionf f with-I l1 electrolytieallycoating ferrou'smetal'strip with tin; although? itisto be understood that its;y principles "may -be'--v followed 'infv electrolyticaliyf vdepositing othey1` pro'' tective' metals on fsti'ips of other conductive`=ma1- terials.v`l

This finvention is concerned' with ther-electro;I plating1 process' in which -thestrip` :is-passed' con'l tinuously` across one cell, or a 'seriesvof-fcells,eachv containing a tin anode. i The stripis'pass'e'dacross eachcellvab'ove theianode andfsubstantially"atthelevel fof 'the 'surface of `the electrolyte -ibath Vcon'- tained in thel cell softhat only the bottomsurfac'e of the'strip is plated.V When it 'is desirable to coat' theoposite surfacethe direction of the st'ril'atravelv is reversed' to'fposition theV othersurfaceridown- Wardl'y` and the `stripfis then passed 4acrossfa 'sec-2 ond series l of-lpl'ating: cells in which the other sur! face issimilarlypoated'; 'I'he stripv passesfacross theiplating" cellat a speed of 5001 feet, ori more; perf minute.- Speeds` 'ofCf1,000 itc-11,500 feetperl minute are used inlfmany` presentcommercialfinf stallations.: The electrolyte solution in each cellff ows out of the" cell'fandflusually owsf'across'tlie side Wallsof the cell that are'located l'faltsucha"A level as to'maintainf the quiescent levelofvthebathffv avori-slightly above the level ofthe bottomfofthe strip.l Electrolytesolution is.v continuously? fed'f into thecell sloas to replenish the bath and main-'L tain the proper concentratienof"tin'saltsf` in* theAv bath;`

Invi continuouslyl electroplatin'gl ferrousm'etal'? strip with tin commercially,` va persistent source ofr trouble `'has been-fthe formatienior hear/fernepos'itsl ofitin along?thefedgesr-of 'tlie stri f i resultof higher currentdnsity. Anothertr'oublel encountered has been-'the deposition ofelotolyte salts? along the edges-ofltlie upper surface` Dams have been placed across the exit endof th'ecells'othat all; or subs'tantially"all, of vtheLele'ctroplating solution flows out *ofthe cell across'thetop of `the danr stops-thenow ofrsomtibnfirr th :directies er` strip travelsothat'at'the-exitend, the level of thesolutionebuilds up above thesurfac'e ofthelstrip whereby the solution -ows baclralongthe` upper surffcland vaids in wettingthe surface andlpre r venting the deposition of salts on thevuppersurfa'c.- The anodes in the cellshave beenffcarefully arranged" in'an effortto reduce thegincr'easedcurren'tldensity 'and/resulting thickness of tin' along the edg'es'fof-thestrip.` Such-efforts have not meti with entire success for the tin coating hascon-y tinuedto loe"tliirin'eralong themiddle portion of the lstripthan'along the-edge portions. This-has in'creasedlthe amoiintof 'coated strip that hashad-v to be scrapped and has further increased the 'cost il inithat'a heavier Vcoatingfof'tin than inecessary must be deposited along the edge portions rtolpro vide-.the'reduiredamount'of tin on the middle `portion` 'i Ac'cordinglyp'one ofthe' primary objectsof fthe present invention is to prevent or reduce the increased thickness ofthe` tin coating alongthe edgesof electroplated strip.

Another object is continuously toY electroplate strip LWithl a uniform coating vof protective metal that'has-substantially the same-'thickness 'along the middle portion asalong the edge' portions.

A furtherfobjectof the present inventionvis to provide 1an -impro'ved` method of and apparatus for'continuously electroplating ferrous metal strip with a uniform coating oftin' on the bottom' surface' and without thedeposition of electrolyte salts onftlrefupper-"surface.vl

Ihave'disc'overed that the-reduced' thickness` ofi' the'tincoating along the'mid-portion of the stripV isfnot'entirelyr a .result of reduced 'current density` along` thisrportion, but that'the manner in which the electrolyte solution "is discharged intof the electroplatingcelli materially affects the'thi'ckness of thef coating'onth'e bottom surface.v1This is somewhat 4fsurprising l as" it Mhas Ibeen considered y heretofore thatf-t-Wasithe distribution ofthe cur-T rent density which affectsV the fthicknes's of the coatingsandthat` it was only nece'ssaryto main ta'inf absolute uniformity of 'i current density -Vtoi hasleen assumed thatif th'eibath Vvvasl'of uniform concentration that a uniform coating lcould be obtained providing: the current density Wasuni-ii I have found that when continuously electroplating strip, and especially at speeds of about 1,000 feet per minute or more, the strip drags along the solution that is in contact with its bottom surface at a speed greater than the rate of ow of the solution inwardly toward the middle of the strip. As a result, there is apparently'a void or depression formed in the solution at a Zone midway of the sides of the strip adjacent the entry end of the cell. The exact nature of what takes place in the solution below the middle of the bottom surface vcan not be visually observed but the answer which I have discovered to the problem indicates that this zone of reduced contact has been the difculty. It has been found that if all of the electrolyte solution which is discharged into` the cell below the level of the strip is discharged inthe form of a single stream directed upwardly kagainst the bottom surface at the middle of the strip width and adjacent the entry end o f the cell, the void is filled and a more uniform coating is obtained and the middle portion of the surface has a coating of about the same thickness as` the edge portions.

The present invention and its objects and advantages will become more readily apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

Figure 1 is a plan view of a portion of an electroplating line including an electroplating cell embodying the principles of the present invention:

Figure 2 is a sectional view taken along line 2-2 of Figure 1;

Figure 3 is a transverse sectional view taken along line 3-3 of Figure 2 with some parts omitted for a better understanding of the present invention.

Referring more particularly to the apparatus shown in the accompanying drawings, a, ferrous metal strip Ill is continuously moved from left to right along the electroplating line and passes from a preceding cell II between an upper contact roll I2 and a lower backup roll I3. The strip I then passes across the cell I4 and between an.upper contact roll I5 and a lower backup roll I6 to a succeeding cell I8. The rotatable contact rolls I2 and I5 are connected to a source of electric current (not shown) and the backup rolls I3 and I6 are usually formed of rubber. The rolls may be power-driven but ordinarily, the strip I0 is continuously moved -along the line by any one of the usual power-actuated roll means customarily used in mills for continuously moving strip along a path.

After the strip I0 leaves rolls I2 and I3, it passes across cell I4 from the entry end to the exit end and has a layer of protective tin deposited on its bottom surface. Cell I4 is similar to the other cells in the electroplating line and may be the rst, last or intermediate one of a series of cells or may be the only cell for plating the bottom surface of the strip. Cell I4 includes a tray I9 supported by the frameworkv 20 and containing an open, plating bath of electrolyte solution I1, Figure 3. The term open means that the upper surface of the bath is free so that the strip can drag solution from the entry end of the tray to the exit end of the tray. The cell tray I4 contains a tin anode formed of a plurality of tin anode elements or bars 2I each having one end supported on a conductive member 22. spaced insulated members 23 are provided in tray I9 for supporting the other ends of the anode elements 2|. Conductive member 22 is provided at one end with bus bars 25 adapted to be connected to the source of electricity to complete the electroplating circuit. The upper. anode-supporting surfaces of the conductive member 22 and insulatedv members 23 extend transversely of the direction of strip travel and these anode supporting surfaces are inclined so that the anode elements can be moved up these surfaces as they erode as a result of the electrodeposition of the anode metal on the bottom surface of strip I0. New anode elements are inserted at 21 (Figures 1 and 3) and eroded elements are removed vat 28. Normally the anode elements are positioned so that the upper surfaces are located in a plane substantially parallel to the strip and so that the width of the anode is substantially the same as the width of the strip to produce a substantially uniform current density across the strip surface.

.The tray includes a. side wall 30 at the entry end which terminates slightly below the pass line of the strip. The level of the sidewall 30 controls the level of the bath in the tray for any one rate of flow of solution into the tray and at any one speed of strip travel. Solution is fed into the tray I9 as will be more fully hereinafter described. The top of sidewall 30 is such that the level of the surface of the bath of solution in the tray with the strip I0 stationary would be at or slightly above the level of the bottom surface of the strip as is indicated in Figure 3. The strip preferably should just touch the bath but to insure contact between the bath and the strip surface, the bath surface often is maintained slightly above this level. The rapidly moving strip I0 drags solution along toward the rolls I5 and I6 and means are provided to confine the solution dragged along by the strip and force the solution flowing out of the cell to flow across the top of sidewall 30 in a direction opposite the -direction of strip travel. The walls at 3| and 32 at opposite sides of tray I9 extend upwardly above the strip far enough to prevent the ow of solution laterally over their tops. The exit end wall 33 is provided witha resilient member 34 which substantially fluid-tightly engages the lower roll I6. Extensions 35 are provided for walls 3I and 32 that extend forwardly to the rolls I5 and I6. Thesolution dragged along the upper surface of the strip cannot flow past the contact roll I5 and builds up in front of the roll. When this dragged solution builds up to a sufiicient height, it flows rearwardly and across the top of wall 30. Trays 36 are provided between the adjacent portions of the cells to catch the solution flowing across wall I9 and to catch the relatively small amount of solution which leaks past the rolls and other elements at the exit side of the tray. This collected solution may be pumped back into the cells. Before pumping the solution into the cells, additions are made'tov the solution to maintain the proper concentration of salts in the bath.

Fresh solution is flowed into tray I9 to replenish the bath and to replace the solution flowing out of the tray. Heretofore, the replenishing solution has been added in a haphazard manner to the cell at a point or points either above or below the strip.

In the present apparatus a flanged tube 31 is fastened to the side 3l of tray I9 and is connected through nipple 38 to one leg of a T connection 39. Al second, upper bent'tube4q is the anode. along the solution immediately adjacentthe strip A .valve 4 I isprovided for controlling theY rate of :flow through tube 40. Theoutlet portion 42 Vof tube 31 terminates in a .single .outlet orice at 43. The outlet portion 42V is bent, upwardly; and is so positioned that 4the streamissuing; from the outlet orifice is directed upwardlyagainst the bottom surface on a zoneat the; middlefoffthe sides of the strip and adjacent the entryof. the cell tray. The zone where the stream from outlet orifice 43 impinges is .ahead vof .theanode so that this stream impingeswagainst the .strip surface before the surface passes across and above The movingr strip apparently drags to form a Void beneath thefstrip. This void may have the conguration indicatedlby the broken line 44 on Figure 3-depending on the rate of travel' of the strip and otherfaetors. `When this void is present, there is a zone of no Contactl with :the strip and the bath which results in a zone of reduced thickness of tin. The reduction in thickness of the tin along the middle portion of the bottom surface is a function of therate of travel cf the strip and is more :pronounced at speeds of about 1,000 feet perminuteY or higher. Regardless of the exact nature of the cause of the decreased thickness of tin along the middle of the strip, it has beenfound that directing the electrolyte solution up againstY a zone midway of the strip and adjacent the entry end of the tray, reduces the difference between the thickness of the tin coating adjacent the edges and at the center and apparently lls this void. Forexample, samples were taken of continuously plated strip. Part of the plated strip was quarterpound plate and the remainder was-half-pound Y plate. A portion of the strip yof `each vweight was plated in accordance with the presentprocess in which all of the electrolyte solution added to the cell at a point below the stripv was directed as a single stream upwardly against the bottom'surface in a rone midway of the strip sides-and -adjacentthe entry end of' the cell. The remainder of the strip was plated'under the same conditions except that the solution-was added in a customary manner to the cell as -shown in the Rieger et al. Patent No.v 2,399,254. The following sets forth the results obtained in which the quantities are in pounds of tin per base box:

.-Thew stream of .solution directed Vupwardly portion.. If the strip were not present, the stream ratecof flow of this upwardly directed stream can be varied, at least to a certain extent, by 10F means of valve 4l. The outlet orifice at 43 is circular, but especially when relatively wider .1 strip is being plated, the outlet oriceA maybe `widened. so as to extend laterally agreater. distance than the orice extends in thev'lirection of strip travel. I claim: .11. In apparatus for progressively electroplatringA only the bottom surface of strip with protective'metal while the strip is continuously moving along a path, said apparatus comprisingan theV path of the strip, sidewalls at opposite sides of the tray means extending above the pathaof the strip, and wall means at vthe exit end of the tray means extending above the path ofthe strip --whereby substantially all of thesolution circulating through the cell lflows rearwardlyacross the top of the wall at the entry end of thecell `.in a direction countercurrently to the direction vof strip travel; a soluble anode of protective metal in the tray means below the path of the strip; means connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and horizontally moving the strip forwardly along such path across the tray'from the entry vend to the exit end with the bottom of the surface in contact with the bath and above the anode at a speed of at least 1,000 feet per minute where- -Vbyy only the bottom surface is electroplated with anode metal; and means for discharging electroplating solution into said ytray and against said strip, said last mentioned means consisting-of means including an outlet positioned abovev the Ipath of the strip arranged to discharge electroplating solution onto the top surface of the strip and/consisting of means extending into the tray below the path of the strip and having a single #outlet orifice positioned below the path of-the Strip coated in accordance 'with present invention The above figures show the great improvement in the uniformity of the thickness of the tin coating obtained with the present invention.

This not only reduces the number `of rejects but also reduces the cost in that it is not necessary to plate the edge portonsexcessively to obtain the strip between the anode and the wall at the entry end of the tray and arranged to discharge a single stream of electroplating solution upwardly against the bottom surface of the strip in a zone at the middle of the strip width adjacent the entry end of the tray and ahead of the anode.

i 2-,1 .nlapcaretus i014 progressively eletropleting only the bottom surface of continuously moving strip with protective metal, said apparatus comprising an electroplating cell including tray means adapted to confine an open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls and wall means at the exit end of the tray means all extending above the path of the strip whereby substantially all of the solution circulating through the cell flows rearwardly across the top of said entry end wall; a soluble anode of protective metal in the tray means below the path of the strip; means for connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and horizontally moving the strip forwardly along a path across the tray means from the entry end to the exit end with the bottom surface of the strip in contact with the bath in the tray and at such a speed that the electroplating solution below the strip is dragged along by the strip toward the exit end of the tray means in an amount suiiicient to form a void in the bath beneath the middle portion of the bottom surface of the strip and the bath solution whereby the protective metal coating along the middle portion is of reduced thickness; and means for discharging electroplating solution into the tray at a point below the strip, said means consisting of a conduit terminating in a single outlet orifice positioned to discharge a stream of electroplating solution upwardly against the bottom surface of the strip in a zone at the middle of the strip width and adjacent the entry end of the tray and ahead of the anode to fill said void with solution whereby the thickness of the protective metal coating along the middle portion of the bottom surface is increased.

3. In apparatus for progressively electroplating only the bottom surface of continuously moving strip with protective metal, said apparatus comprising an electroplating cell including tray means adapted to confine an open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls and wall means at the exit end of the tray means all extending above the path of the strip whereby substantially all of the solution circulating through the cell flows rearwardly across the top of said entry end wall; a soluble anode of protective metal in the tray means below the path of the strip; means for connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and horizontally moving the strip along a path across the tray means from the entry end to the exit end with the bottom of the surface in contact with the bath in the tray and at such a speed that the electroplating solution below the strip is dragged along by the strip toward the exit end of the tray means in an amount sufficient to form a void in the bath beneath the middle portion of the bottom surface of the strip and the bath solution whereby the protective metal coating along the middle portion is of reduced thickness; and means for discharging electroplating solution into said tray and against said strip, said last-mentioned means consisting of means including an outlet orifice positioned above the path of the strip arranged to discharge electroplating solution onto the top surface of the strip and consisting of means having a single outlet orifice positioned below the i .pathY of the strip arranged to discharge a single stream of electroplating solution upwardly against the bottom surface of the strip in a zone at the middle of the strip width and adjacent the entry end of the tray and ahead of the anode.

4. In apparatus for progressively electroplating only the bottom surface of continuously moving strip, said apparatus comprising an electroplating cell including tray means adapted to confine an'open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls and wall means at the exit end of the tray means all extending above the'path of the strip whereby substantially all of the solution circulating through the cell flows rearwardly across the top of said entry end wall; a soluble anode of protective metal in the tray below the path of the strip; means for connecting the anode and the strip to a source of electro- 'plating current as anode and cathode, respectively; means for supporting and horizontally moving the strip along a path at a speed of at least 1,000 feet per minute across the tray means from the entry end to the exit end with the bottom of the surface in contact with the bath in the tray whereby electroplating solution below the strip is dragged by the strip from the entry end toward the exit end of the tray means in an amount sufficient to form a void in the solution below the middle of the bottom surface of the strip adjacent the entry end of the tray; and means for discharging electroplating solution into the tray at a point below the strip, said means consisting of a conduit means terminating in a single outlet orice positioned to discharge a stream of electroplating solution upwardly against the bottom surface of the strip in a zone at; the middle of the strip width and adjacent the entry end of the tray and ahead of the anode to ill said void with solution whereby the thickness of the protective metal coating along the middle portion of the bottom surface is increased.

5. In apparatus for progressively electroplating the bottom surface of continuously moving strip, said apparatus comprising an electroplating cell including tray means adapted to conne an open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls andV wall means at the exit end of the tray means all extending above the path of the strip whereby substantially all of the solution circulating through the cell flows rearwardly across the top of said entry end wall; a soluble anode of protective metal in the tray means below the path of the strip; means for connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and hori- Zontally moving the strip along a path at a speed of at least 1,000'feet per minute across the tray means from the entry end to the exit end 1' with the bottom of the surface in contact with the bath in the tray means whereby electroplating solution below the strip is dragged by the charge electroplating solutioneontoethe top surface.- of fthestripandfconsisting of means having a single outlet orifice positioned below the path of the strip arranged to discharge a single stream of electroplating solutionl lupwardly against the bottom surfacerin a zone at themiddle oi'the strip width` andadjacent the entry,l end of the tray and ahead of the anode to ll said void.

V6. Inapparatus for progressively electroplating only the -bottom-- surface of continuously horizontally moving' strip, `said-apparatus comprising anelectroplatingcell 'including a tray adapted to contain--an openi bathy of electroplating solution, an anode -of protectivemetal in the tray below the path of the strip, and means causing thesolution to flow fromthe tray only at the entry end"of"the"tray" andonly in a direction opposite to the direction of strip travel; means for connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and horizontally moving the strip at a speed of at least 1,000 feet per minute across the tray from the entry end to the exit end with the bottom surface of the strip in contact with the surface of the bath in the tray whereby the bottom surface is plated with anode metal and the electroplating solution below the strip is dragged in the direction of strip travel to tend to form a zone of reduced contact between the middle portion of the strip bottom surface and the bath solution adjacent the entry end of the tray; and means for discharging electroplating solution into said tray and against said strip, said means consisting of means including an outlet orice positioned above the path of the strip, arranged to discharge electroplating solution onto the top surface of the strip and consisting of means having a single outlet orice positioned below the path of the strip arranged to discharge a single stream of electroplating solution upwardly against the bottom surface in a zone at the middle of the strip width and adjacent the entry end of the tray and ahead of the anode to fill said void.

7. In the process of progressively and continuously electroplating the bottom surface of continuously moving strip with protective metal, the steps comprising supporting and horizontally moving the strip along a horizontal path across an electroplating cell containing an open bath of electrolyte solution and a soluble anode of protective metal with the strip bottom surface in contact with the surface of the bath and above the anode while the strip is connected as a cathode to a source of electroplating current and while electrolytically depositing protective metal coating only on the bottom surface; and discharging electrolyte solution against the strip in the form of two streams only, and directing one stream against the upper surface of the strip and directing the other stream upwardly against the bottom surface in a zone at the middle of the strip width and adjacent the entry end f the cell and ahead of the anode.

8. In apparatus for progressively electroplating, only the bottom surface of continuously moving strip with protective metal, said appara tus comprising an electroplating cell including tray means adapted to confine an open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls and wall means at the exit end of the tray all extending above the path `of the` strip whereby substantially all of the solution; circulating;v through the cell flowsrearwardly across theltop.:

of said entry end wall; a solubleanode'aof proanode and cathode, respectfully; meansffor supporting andV horizontally moving the --strip forwardly along apath across the Vtray-from the,Y

entry end to the exit end with the bottom surface 'of the strip in contact with; thebath in the tray so that onlythef'bottom surface is plated with anode metal; and means-for discharging" electroplating solutionY into the tray belowj thepath ofthe strip, said last ,mentioned means-terminating in a single outlet orificepositioned adjacent theentry end oftheV tray and@ ahead' of;y

the anode and below the path of the strip and said outlet orifice being positioned to discharge a stream of electroplating solution upwardly against the bottom surface of the strip in a zone at the middle of the strip width and adjacent the entry end of the tray and ahead of the anode.

9. In apparatus for progressively electroplating only the bottom surface of continuously moving strip with protective metal, said apparatus comprising an electroplating cell including tray means adapted to confine an open bath of electroplating solution, said tray means having an upwardly extending wall at its entry end terminating below the path of the strip, sidewalls and wall means at the exit end of the tray means all extending above the path of the strip whereby substantially all of the solution circulating through the cell fiows rearwardly across the top of said entry walls; a soluble anode of protective metal in the tray below the path of the strip; means for connecting the anode and the strip to a source of electroplating current as anode and cathode, respectively; means for supporting and horizontally moving the strip forwardly along a path across the tray from the entry end to the exit end with the bottom surface of the strip in contact with the bath in the tray so that only the bottom surface is plated with anode metal; and means for discharging electroplating solution into said tray and against said strip, said last mentioned means including an outlet orice positioned above the path of the strip arranged to discharge electroplating solution onto the top surface of the strip and a single outlet orifice positioned below the path of the strip adjacent the entry end of the tray and ahead of the anode, the outlet orifice positioned below the path of the strip being positioned to discharge a single stream of electroplating solution upwardly against the bottom surface of the strip in a zone at the middle of the strip width and adjacent the entry end of the tray and ahead of the anode.

10. The process claimed in claim 'I in which the electroplating cell includes an upwardly extending wall at its entry end terminating below the path of the strip and which includes the step of flowing across the top of the entry end wall in direction opposite to the direction of strip movement substantially all of the electrolyte solution circulating through the cell.

1l. In the process of progressively and continuously electroplating the bottom surface of continuously moving strip with protective metal, the steps comprising supporting and horizontally moving the strip along a horizontal path across an electroplating cell from entry end to exit end, the cell including a tray containing an open bath of electroplating solution and a soluble anode of protective metal and having an upwardly extending wall at the entry end of the tray terminating below the path of the strip, the strip being moved across the cell with the strip bottom surface in contact with the surface of the bath and above the anode while the strip is connected as a cathode to the source of electroplating current and while eleetrolytically depositing a protective metal coating only on the bottom 'surface and While flowing electrolyte solution from the tray only across the top of the entry end wall in a direction opposite the direction of strip travel; and discharging electrolyte solution into the tray at a level below the path of strip travel and directing all of this electrolyte solution in the form of a single stream upwardly against the bottom surface in a. zone at the middle of the strip width and adjacent to the entry end ofthe tray'and4 ahead of the anode.

' HARRY J. READING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. IN APPARATUS FOR PROGRESSIVELY ELECTROPLATING ONLY THE BOTTOM SURFACE OF STRIP WITH PROTECTIVE METAL WHILE THE STRIP IS CONTINUOUSLY MOVING ALONG A PATH, SAID APPARATUS COMPRISING AN ELECTROPLATING CELL INCLUDING OPEN TRAY MEANS ADAPTED TO CONFINE AN OPEN BATH OF ELECTROPLATING SOLUTION, SAID TRAY MEANS HAVING AN UPWARDLY EXTENDING WALL AT ITS ENTRY END TERMINATING BELOW THE PATH OF THE STRIP, SIDEWALLS AT OPPOSITE SIDES OF THE TRAY MEANS EXTENDING ABOVE THE PATH OF THE STRIP, AND WALL MEANS AT THE EXIT END OF THE TRAY MEANS EXTENDING ABOVE THE PATH OF THE STRIP WHEREBY SUBSTANTIALLY ALL OF THE SOLUTION CIRCULATING THROUGH THE CELL FLOWS REARWARDLY ACROSS THE TOP OF THE WALL AT THE ENTRY END OF THE CELL IN A DIRECTION COUNTERCURRENTLY TO THE DIRECTION OF STRIP TRAVEL; A SOLUBLE ANODE OF PROTECTIVE METAL IN THE TRAY MEANS BELOW THE PATH OF THE STRIP; MEANS CONNECTING THE ANODE AND THE STRIP TO A SOURCE OF ELECTROPLATING CURRENT AS ANODE AND CATHODE, RESPECTIVELY; MEANS FOR SUPPORTING AND HORIZONTALLY MOVING THE STRIP FORWARDLY ALONG SUCH PATH ACROSS THE TRAY FROM THE ENTRY END TO THE EXIT END WITH THE BOTTOM OF THE SURFACE IN CONTACT WITH THE BATH AND ABOVE THE ANODE AT A SPEED OF AT LEAST 1,000 FEET PER MINUTE WHEREBY ONLY THE BOTTOM SURFACE IS ELECTROPLATED WITH ANODE METLA; AND MEANS FO RDISCHARGING ELECTROPLATING SOLUTION INTO SAID TRAY AND AGAINST SAID STRIP, SAID LAST MENTIONED MEANS CONSISTING OF MEANS INCLUDING AN OUTLET POSITIONED ABOVE THE PATH OF THE STRIP ARRANGED TO DISCHARGE ELECTROPLATING SOLUTION ONTO THE TOP SURFACE OF THE STRIP AND CONSISTING OF MEANS EXTENDING INTO THE TRAY BELOW THE PATH OF THE STRIP AND HAVING A SINGLE OUTLET ORIFICE POSITIONED BELOW THE PATH OF THE STRIP BETWEEN THE ANODE AND THE WALL AT THE ENTRY END OF THE TRAY AND ARRANGED TO DISCHARGE A SINGLE STREAM OF ELECTROPLATING SOLUTION UPWARDLY AGAINST THE BOTTOM SURFACE OF THE STRIP IN A ZONE AT THE MIDDLE OF THE STRIP WIDTH ADJACENT THE ENTRY END OF THE TRAY AND AHEAD OF THE ANODE. 